Abstract
Background: The objectives of this study were to determine whether
intramedullary reaming increases bone temperature in vivo to a level that is
high enough to produce bone necrosis and to determine the influence of the
size and the condition of the reamers on the temperature increase.
Methods: Bone temperature variations were recorded in vivo during
intramedullary tibial reaming in fourteen minipigs. The left tibiae were
progressively reamed from 6 to 9 mm. The right tibiae were reamed with only 8
and 9-mm reamers. The variables studied were the initial and final temperature
and the increase in the temperature. Two weeks after reaming, the tibiae were
removed and studied histologically.
Results: Intramedullary reaming produced an average increase (and
standard deviation) in bone temperature of 6.9°C ± 4.1°C. The
peak temperatures ranged from 34.9°C to 49.4°C. The average maximum
bone temperature was 38.1°C ± 2.8°C when the reaming was done
progressively from 6 to 9 mm and 41.1°C ± 4.4°C when the
reaming was done only with the 8 and 9-mm reamers. The mean increase in the
temperature in the second group of animals (8.2°C ± 4.3°C) was
greater than that in the first group (5.4°C ± 3.5°C). Reaming
with sharper reamers in the first seven animals resulted in a smaller mean
increase in temperature than did reaming with less sharp reamers in the last
seven animals (4.6°C compared with 9.2°C; p = 0.001). Histological
examination of the tibiae showed periosteal proliferation and an altered
disposition of the osteons at the inner cortex with occasional necrotic bone
fragments in the medullary canal.
Conclusions: Intramedullary reaming in the minipig increased bone
temperature. When the reamer initially used was larger than the diameter of
the medullary canal and when the reamers were blunted by repeated use, the
maximum temperature reached by the bone was higher. This increase in
temperature with use of typical medullary reaming techniques did not exceed
the limits that would produce bone necrosis.
Clinical Relevance: Use of appropriately sized reamers in good
condition reduces the increase in bone temperature that occurs during
intramedullary reaming.
Intramedullary reaming is a popular procedure in orthopaedic surgery and
traumatology. It increases the contact area between bone and implant,
providing more stable fixation and allowing for the use of larger and stronger
implants that are less likely to fail by
fatigue1,2.
It also promotes fracture-healing by creating graft at the fracture
site3,4.
Complications that have been described after the use of reaming include the
destruction of the endosteal blood
supply5, increased
intramedullary
pressure6,7,
decreased bone
strength3,
embolization of bone marrow
contents8, increased
intracranial pressure in patients with a concomitant head
injury9, and
increased bone
temperature10-13.
A review of the literature on the effect of the increase in bone
temperature during
reaming10-15
showed that these studies had been largely conducted on cadaveric bone or saw
bones. They suggested theoretical conclusions about the extent and the type of
bone damage that the temperature increase could produce, but they did not take
into account other parameters that could influence an in vivo experiment, such
as the cooling effect of the vascular system and
bleeding16. We know
of no study that has documented, with histological analysis, whether bone
necrosis can occur in living bone during reaming.
The goals of this study were to determine whether intramedullary reaming
increases bone temperature in vivo to a level that is high enough to produce
bone necrosis and to determine the influence of the size and the condition of
the reamers on the temperature increase.
Bone temperature variations were recorded in vivo during intramedullary
tibial reaming in fourteen minipigs with the use of a thermal probe (model RTD
Pt 100; Adaba Ingenieros, Madrid, Spain). The probe was 3 mm in diameter and
50 mm long, and it had a temperature range of —200°C to
850°C.
The probe was introduced through a 3.2-mm hole drilled in the middle third
of the anteromedial part of the tibia. After drilling the cortex, we measured
the cortical bone thickness with an AO measuring guide and then placed the
probe within 1 mm of the endosteal bone surface
(Fig. 1). Küntscher
reamers (Bixcut; Stryker Trauma GmbH, Kiel, Germany) that were 6, 7, 8, and 9
mm in diameter were used. The cutting portion of the reamers was 12 mm long.
The maximum speed of the drill was 1500 rpm. Temperature was recorded every
three seconds throughout the surgical procedure. The average time (and
standard deviation) of each reaming was 31.7 ± 4.3 seconds. The data
were sent to a personal computer through a sixteen-bit analog-digital
converter and were stored by a temperature acquisition program designed
specifically for this study in a Windows environment. The accuracy of the
temperature recordings was within 0.1°C.
The surgical procedures were done with the animals under general
anesthesia. A standard operative technique was
used1. The left
tibiae were progressively reamed from 6 to 9 mm, and the right tibiae were
reamed only with the 8 and 9-mm reamers to produce more cutting torque.
Radiographs were made before and after the surgical procedure.
Preoperatively, the medullary canal was measured on anteroposterior and
lateral radiographs. The average diameters of the medullary canals were 7.6
× 5.4 (range, 6 × 5 mm to 10 × 7 mm). The postoperative
radiographs showed that the reaming had extended beyond the narrowest part of
the medullary canal.
Postoperatively, the animals went to a room in the vivarium and were placed
under the care of the veterinarians. After two weeks, the animals were killed,
the tibiae were removed, and the middle third was fixed in 10% formaldehyde.
After decalcification and embedding in paraffin, transverse cuts of
approximately 8 µm in thickness were made at the middle third of each
tibia. The cuts were stained with hematoxylineosin and Masson trichrome stain
for examination with optical microscopy.
The variables studied were the initial temperature, the maximum
temperature, and the increase in the temperature, measured in degrees Celsius,
in each limb of each animal. The values for the right and left sides were
compared. In addition, the first fourteen reamings were compared with the last
fourteen reamings to examine the effect of the repeated use of the
reamers.
The normality of the variables was tested with the Kolmogorov-Smirnov test.
The Student t test for dependent measures was used to compare the temperatures
before and after reaming. The Student t test for independent measures or its
nonparametric equivalent, the Mann-Whitney test, was used to compare the
temperatures and any increase related to the type of reaming and the condition
of the reamers.
The significance level was p < 0.05. The statistical analysis was
performed with the SPSS for Windows (version 9; SPSS, Chicago, Illinois).
Intramedullary reaming produced an average increase (and standard
deviation) in bone temperature of 6.9°C ± 4.1°C. Peak
temperatures ranged from 34.9°C to 49.4°C (see Appendix). The average
maximum temperature recorded was 38.4°C ± 2.9°C in the first
seven minipigs and 40.8°C ± 4.6°C in the last seven
animals.
We compared the maximum temperature and the increase in the temperature
when the reaming was done progressively from 6 to 9 mm on the left side and
when the reaming was done only with the 8 and 9-mm reamers on the right side.
The average maximum temperature obtained during reaming was significantly
greater when the reaming was done directly with the 8 and 9-mm reamers
(41.1°C ± 4.4°C) than when the reaming was done progressively
from 6 to 9 mm (38.1°C ± 2.8°C) (p = 0.04). A difference in the
average increase in the temperature between the two groups was observed
(5.4°C ± 3.5°C with the progressive reaming compared with
8.2°C ± 4.3°C with the 8 and 9-mm reamers), but it was not
significant (p = 0.07) with the numbers available.
To examine the effect of repeated use of the reamer, we compared the
increase in the temperature for the first fourteen reamings with that for the
last fourteen reamings. The mean increase in the temperature for the last
fourteen reamings was significantly greater (9.2°C ± 4.2°C)
than that for the first fourteen reamings (4.6°C ± 2.3°C) (p =
0.001).
Histological Analysis
Histological examination of the tibiae at two weeks showed changes in the
normal architecture of the subperiosteal bone, the internal cortices, and the
endomedullary region.
Histological sections of both the left and the right tibia demonstrated
periosteal proliferation with evidence of underlying mature, well-organized
trabecular osteoid, oriented perpendicular to the outer cortex
(Fig. 2). The outer diaphyseal
cortex appeared to be intact. The inner diaphyseal cortex demonstrated an
altered disposition of the osteons, which were surrounded by remodeled bone
with deposits of new osteoid. We also observed areas of bone resorption with
piecemeal bone necrosis, scar tissue, hematoma, and free bone fragments with
an irregular presence of osteocytes (Fig.
3).
In the medullary canal, there were necrotic bone fragments with irregular
basophilic edges, fat-tissue necrosis, blood clots, and an absence of
osteocytes in the bone lacunae. Surrounding the bone fragments, we found
fibrin, inflammatory cells, fibroblasts, and stroma, which are typical of
immature fibrous reparative tissue.
In the left tibiae, we observed disorganized immature osteoid that was
lined up in thin sheets or in irregular strands of fibrous immature bone
tissue. In the right tibiae, we observed immature fibrous osteoid that was
somewhat more organized.
Minipig bone has more mineralized bone tissue and a greater bone density
than human bone and, therefore, it has greater mechanical
strength17. The
maximum bone temperature obtained has been reported to be directly related to
the angular velocity of reaming so that greater angular velocities produce a
greater increase in bone
temperature16,18.
We used an electrical motor that can produce a gradual and controlled increase
in angular velocity of up to 1500 rpm. In the clinical setting, the motors
usually work with top speeds of approximately 800 rpm.
Considering these two points, it seems logical that the temperatures
produced by reaming in humans should be lower than those measured in our
study. However, the maximum temperatures recorded in our study, which varied
between 34.9°C and 49.4°C, are very similar to the ones recorded by
Giannoudis et al.19
in human tibiae (range, 36.1°C to 51.6°C). Although they did not
report the average temperature, they noted that seventeen tibiae that had been
reamed had a maximum temperature of <46.1°C.
Baumgart et
al.13, in a
theoretical model of intramedullary reaming, established that heat flow exists
between the bone and the reamer and that it can be described in terms of a
thermal conductivity equation. The parameters considered were the angular
velocity of the reaming process, the degree of friction, the size of the
medullary canal, the size of the reamer, and the thermal conductivity. They
concluded that the maximum temperature occurs in the area of bone in direct
contact with the reamer end and that, at a distance of 2 mm from the reamer,
the recorded temperature can drop by 4°C.
In our experimental model, the thermal probe was placed 1 mm away from the
endosteum, perpendicular to the long axis of the medullary canal and in the
middle third of the diaphysis, where the canal is narrowest and therefore
where more reaming takes place. As has been noted in other
studies10,19,
the recorded temperatures at that point should be very close to the true
intramedullary temperature because of the close position of the probes to the
heat source.
Henry et al.10
studied intramedullary temperatures recorded by reaming twelve cadaveric
tibiae and five cadaveric femora. They started reaming with an 11-mm-diameter
reamer and reamed up to 15 mm in 1-mm increments. The average temperature was
52°C ± 8.3°C (range, 42°C to 67°C). They found a
substantial increase in the intramedullary temperature because of reaming.
Müller et
al.15 also found an
increase in the temperature of cortical bone after reaming five pairs of human
cadaveric femora, although the maximum temperature recorded was slightly lower
(44.1°C). Those studies were done in vitro, which may have produced
different results from those of in vivo testing because of two major factors.
First, in vitro bone has less specific heat than in vivo bone because it has
less water content; therefore, less energy is required to produce a
temperature
increase10. Second,
the cortical vascular system and, above all, bleeding could act as a
refrigerating system, dissipating the thermal energy that originates during
the reaming
process16.
Our results confirm that reaming does produce an increase in bone
temperature. It is important to note that the temperatures recorded in this
study were lower than those reported for cadaveric
bone10,13-15
and they were in a range that is unlikely to produce bone necrosis.
One of the factors that seems important in determining the maximum bone
temperature during intramedullary reaming is the size of the reamer compared
with the size of the medullary canal. The bigger the reamer or the smaller the
diameter of the medullary canal, the greater the work required to cut the bone
and, therefore, the higher the generated
temperature10,13,20.
Müller et
al.15, when reaming
five human cadaveric femora, established that variations in the temperature of
the medullary canals were greater during the initial phase of the reaming
process than in the later phases because of the initial variation in the canal
width. Giannoudis et
al.19 found a
significant increase in temperature when comparing an 8-mm-diameter medullary
canal reamed with a 10-mm reamer and a 9, 10, or 11-mm-diameter medullary
canal reamed with the same 10-mm reamer (analysis of variance, p = 0.01).
We performed vigorous reaming of the right tibiae starting directly with
the 8-mm-diameter reamer (the average size of the right tibial medullary
canals was 7.7 × 5.1 mm). The average maximum temperature registered was
41.1°C ± 4.4°C, and the average increase in the temperature was
8.2°C ± 4.3°C. A similar condition could occur clinically when
the medullary canal is narrow and an appropriately sized reamer with a smaller
diameter to match the canal diameter is not available. The maximum temperature
obtained when the reaming commenced directly with the 8-mm-diameter reamer was
higher (p = 0.04) than that obtained when the reaming was begun with use of
the 6-mm-diameter reamer.
The condition of the cutting edge of the reamer is another factor that has
been related to the increase in the temperature during reaming. Müller et
al.15 compared
temperatures when reaming five pairs of cadaveric femora with new reamers and
when reaming femora with reamers worn down by use. They found that the maximum
temperature produced by the used reamers (44.1°C) was significantly higher
(p < 0.05) than that produced by the new reamers (39.5°C). Baumgart et
al.13 concluded
that a sharp cutting edge is the most important factor in controlling the
increase in bone temperature during reaming and that blunt reamers should be
retired from clinical use. We found a significant difference in temperature
increase (p = 0.001) due to reamer wear, after even as few as fourteen
reamings. One of the factors that could influence these results is the high
mineral content of minipig
bone17, perhaps
resulting in more rapid wear of the reamers.
Lundskog21
described extensive necrosis in cortical bone at temperatures of 70°C. The
temperature threshold at which Matthews and
Hirsch22 found
tissue damage was 56°C, which is the temperature at which alkaline
phosphatase denatures. Eriksson and
Albrektsson23
stated that a constant temperature of 47°C for one minute produced bone
necrosis. Frölke et
al.14 determined
that reaming almost never takes more than forty seconds for each reamer size
and that the average contact time between the reamer and the bone is fifteen
seconds. He suggested that temperatures of =77°C during reaming would
be safe for bone tissue because of the brief exposure. Giannoudis et
al.19 also did not
find evidence that, in normal situations, the increase in temperature produced
by reaming is high enough to result in bone necrosis. In our study, all
temperatures recorded for the bones were <50°C, which was lower than
that considered a risk for bone necrosis. The histological changes were
similar in all the specimens and were not related to the maximum temperature
obtained and demonstrated little or no evidence of thermally induced bone
necrosis.
A table showing all temperatures recorded in the study is available with
the electronic versions of this article, on our web site at
(go to the article citation and click on "Supplementary Material")
and on our quarterly CD-ROM (call our subscription department, at
781-449-9780, to order the CD-ROM).
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